**Core Concept:** Puberty is a critical stage in human development where the body undergoes significant changes to prepare for reproduction. During puberty, the process of endochondral bone growth in long bones is accelerated, leading to increased bone length and strength. This process is primarily regulated by hormones.

**Why the Correct Answer is Right:** Osteocalcin is a hormone primarily responsible for skeletal maturation during puberty. It is produced by osteoblasts, the cells responsible for bone formation, and acts on osteoclasts, cells responsible for bone resorption. Osteocalcin stimulates osteoclasts to release calcium from the bone matrix into the bloodstream, which increases blood calcium levels. This increase in blood calcium levels activates the hypothalamic-pituitary-gonadal (HPG) axis, triggering sexual maturation and the onset of puberty.

**Why Each Wrong Option is Incorrect:**

A. Osteocalcin is correct, so this option is incorrect.
B. Osteocalcin is responsible for bone maturation, making this option incorrect.
C. Insulin-like growth factor I (IGF-I) is involved in growth and development, but not specifically for bone maturation during puberty.
D. Growth hormone (GH) plays a role in overall growth, but not specifically for bone maturation during puberty.

**Clinical Pearl:** Osteocalcin is a key hormone in regulating bone maturation during puberty. A deep understanding of osteocalcin and its role in the HPG axis is essential for medical students and practicing physicians alike, as it impacts the diagnosis and treatment of conditions involving bone disorders and puberty onset.